Gas turbine bucket

ABSTRACT

In a gas turbine bucket, having a blade and a root, composed of a eutectic alloy the blade is reinforced by eutectic fibers disposed in grain-orientated form, whilst in the root of the bucket the structure is non-orientated and enjoys a desirably high impact strength and ductility.

United States Patent [1 1 Endres GAS TURBINE BUCKET [75] Inventor:Wilhelm Endres, Ennetbaden, Switzerland [73] Assignee:Aktiengesellschaft Brown, Boveri &

Cie, Baden, Switzerland [22] Filed: Apr. 5, 1972 [21] Appl. No.: 241,165

[30] Foreign Application Priority Data Apr. 8, 1971 Switzerland 5225/71[52] US. Cl. 416/241 [51] Int. Cl. Fold 5/28 [58] Field of Search416/241; 164/60, 122, 125, 164/127 [56] References Cited UNITED STATESPATENTS v 2,422,193 6/1947 Hague 416/241 UX Feb. 5, 1974 3,044,7467/1962 Stargardter 416/241 3,260,505 7/1966 Ver Snyder... 416/214 X3,342,455 9/1967 Fleck et al. 416/241 3,494,709 2/1970 Piearcey 416/241X Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, orFirm-Ralph B. Parker et al.

[5 7] ABSTRACT In a gas turbine bucket, having a blade and a root,

composed of a eutectic alloy the blade is reinforced by eutectic fibersdisposed in grain-orientated form, whilst in the root of the bucket thestructure is nonorientated and enjoys a desirably high impact strengthand ductility.

4 Claims, 2 Drawing Figures 1 GAS TURBINE BUCKET This invention relatesto turbine buckets, and is concerned with the development of quitedifferent properties in different parts of the bucket, the chemicalcomposition of the metal in the bucket being the same in both blade androot.

The prior art discloses gas turbine buckets which are reinforced byeutectic fibers, solidified in grainorientated form. They suffer fromthe disadvantage of having only a low notch impact strength. While a lownotch impact strength in the blade of the bucket does not result in anysubstantial disadvantages, the bucket root itself suffers from theserious disadvantage that it is unable to deform itself sufficiently inthe zone at which it is joined to the rotor.

An object of the present invention is to provide a gas turbine bucket,the blade of which is reinforced in known manner by eutectic fibers buthaving sufficient impact strength in the bucket root.

According to the invention this and other inventive objects are achievedin that in the gas turbine bucket, which is constructed of a eutecticalloy, the crystals embedded in the parent material are formed as fibersdisposed longitudinally in parallel to the bucket blade and extendinginto the bucket root, the bucket root having a non-orientated structure.

The invention will now be explained in greater detail I hereinbelow, andwith reference to the accompanying schematic drawing, in which:

FIG. 1 is a gas turbine bucket in section; and

FIG. 2 is an apparatus forproducing a gas turbine bucket of the-kindillustrated in FIG. 1. FIG. 1 shows a gas turbine bucket 1 comprising abucket blade 2 and a bucket root 3. The gas turbine bucket l is composed'of a eutectic alloy, the bucket blade having been subjected tograin-oriented solidification. The crystals embedded in the parentmaterial 4 take the form of longitudinally parallel fibers 5 extendingfrom the outer end of the bucket blade 2 through the blade and into thebucket root 3. A gas turbine bucket of this kind is constructed asfollows.

A melt of a pseudo binary eutectic alloy Co1 ,,Cr Cr ,Co,C containing inweight percentages, 56.] percent cobalt, 40 percent chromium and 2.4percent carbon, is cast into a precision mold of corundum. The precisionmold 6 is introduced into a graphite succeptor 7 which may beinductively heated by means of a heating spiral 8. To this endtheprecision mold 6 is introduced into the graphite succeptor 7 so that thebucket blade 2 and the upper quarter of the bucket root 3 are disposedin the graphite succeptor 7 while the lower part of the bucket root 3extends from the aforementioned succeptor, as shown in FIG. 2.

The graphite succeptor 7 is heated to a temperature between .1 ,400 andl,600 C. and is maintained at the aforementioned temperature. Since themelting temperature of the alloy is 1,310 C., the melt forming thebucket blade is retained in the superheated, fluid state while thebucket root 3 solidifies. After solidification of the bucket root 3, thegraphite succeptor 7 is moved upwardly in the direction of the arrow andaxially relative to the precision mold 6, the velocity of the saidmotion being between 5 and cm/h. Accordingly, the melt solidifies in theupper quarter of the bucket root 3 and then in the bucket blade 2, thesolidification front moving from the bucket root 3 to the upper end ofthe bucket blade 2. The gas turbine blade may be stripped from the moldas soon as the precision mold 6 has been entirely withdrawn from thegraphite succeptor 7 and the melt has solidified.

By practicing this technique the blade structure is reinforced byeutectic fibers which are solidified in grain-oriented form, whilst inthe root per se of the bucket the structure is non-oriented, as isillustrated in FIG. 1, and has an advantageous ductility at theoperating temperature of the turbine bucket.

The method is also suitable for the following alloys:

' Co, ,,Cr TaC CoTaC Ni, ,,Cr -TaC. I claim: 1. Gas turbine bucketformed of a eutectic alloy and having a root and a bIade,-said bladehaving a crystalline structure oriented in parallel to the longitudinalorientation of the bucket blade whilst in the bucket root the structureis not grain-oriented and is ductile at the operating temperature of theturbine.

2. Gas turbine bucket according to claim 1, in the blade of whichcrystals embedded in matrix are present as fibers disposedlongitudinally in parallel to the blade and extend through the blade andto the root per se.

3. Gas turbine bucket according to claim 1, in which the eutectic alloyis a member of the group of alloys consisting of CoCrC, NbNb C, Ta'Ta C,

Ni-Ni Nb, Ni Ni Ti, NiAlvCr, CoTiC, Ni-TaC,

' the alloy is a CoCrC alloy consisting essentially of 56.1 wt. percentcobalt, 40 wt. percent chromium and 2.4 wt. percent carbon.

2. Gas turbine bucket according to claim 1, in the blade of whichcrystals embedded in matrix are present as fibers disposedlongitudinally in parallel to the blade and extend through the blade andto the root per se.
 3. Gas turbine bucket according to claim 1, in whichthe eutectic alloy is a member of the group of alloys consisting ofCo-Cr-C, Nb-Nb2C, Ta-Ta2C, Ni-Ni3Nb, Ni-Ni3Ti, NiAl-Cr, Co-TiC, Ni-TaC,Co-VC, NiAl-Ni3Nb, Ni3-Al-Ni3Ta, Co1 x-Crx-TaC, Co-TaC, and Ni1x-Crx-TaC.
 4. Gas turbine bucket according to claim 3, wherein the alloyis a Co-Cr-C alloy consisting essentially of 56.1 wt. percent cobalt, 40wt. percent chromium and 2.4 wt. percent carbon.